1. Field of the Invention
The present invention relates to a printed-circuit board, a coaxial cable, and an electronic device, and more specifically to those capable of reducing electromagnetic interference (EMI) which occurs when a current flows in the same direction in a ground pattern and a power supply pattern, both of which are respectively made up of a wide electric conductor pattern and disposed, opposed to each other.
The present application claims priority of Japanese Patent Application No. 2001-188912 filed on Jun. 21, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
An electronic device including various electronic components such as active elements and passive elements is assembled by packaging desirable electronic components on a printed-circuit board. On the printed-circuit board there are formed a ground pattern for providing reference electric potential to the electronic components and a power supply pattern for supplying electric power by making use of electric conductor patterns. Use is sometimes made of a wide electric conductor pattern as such the ground pattern and the power supply pattern. For example, in a printed-circuit board on which an ordinary integrated circuit is packaged there is known wide electric conductor patterns having longitudinal and lateral width sizes of several centimeters.
In such the printed-circuit board, electromagnetic energy is supplied to the wide electric conductor pattern through terminal resistance during operation of the electronic device. A current is hereby conducted to the wide electric conductor pattern to cause resonance, whereby unnecessary electromagnetic waves (so-called xe2x80x9cradiated emissionxe2x80x9d) are radiated from the wide electric conductor pattern to the surroundings.
Radiation of unnecessary electromagnetic waves causes occurrence of EMI, whereby the electronic device is subject to electromagnetic interference.
Occurrence of such EMI is more increased particularly when the wide electric conductor pattern acts as an antenna.
When the ground pattern and the power supply pattern are formed in opposition to each other to permit a current to conduct in the same direction through both patterns, that is to say, a current flows in a same phase through both patterns, both patterns act as if they are a single wide electric conductor pattern, whereby the wide electric conductor pattern acts as an antenna to radiate strong unnecessary electromagnetic waves. Such a current conducted through the wide electric conductor pattern is called a common mode current, and resonance at that time is called a common mode resonance.
Referring here to FIG. 20A the common mode resonance is intensified provided a size of a wide electric conductor pattern 110 in a lateral direction X is set into an elongated configuration. Referring further to FIG. 20B, the common mode resonance is intensified provided the wide electric conductor pattern 110 is formed into a T-shaped pattern by uniting a first electric conductor section 111 and a second electric conductor section 112 both having different longitudinal sizes in a vertical direction Y. Referring furthermore to FIG. 20C, the common mode resonance is intensified when the wide electric conductor pattern 110 is formed into an L-shaped pattern by uniting a first electric conductor section 113 and a second electric conductor section 114 both having different longitudinal sizes in the vertical direction Y.
More specifically, when the wide electric conductor pattern 110 is formed into a pattern configuration having partly a recessed section 115 such as the aforementioned T-shaped pattern or L-shaped pattern for example, the common mode resonance is intensified in particular. Any pattern configuration partly having the recessed section 115 as such is inevitably formed because of limitation to an area of a printed-circuit board on which many electronic components are packaged when the printed-circuit board is manufactured which is then actually assembled into varieties of electronic devices.
Japanese Laid-open Patent Application No. Hei 10-190237 for example discloses a printed-circuit board (first prior art technique) in which EMI occurring owing to the aforementioned common mode current is reduced. FIG. 21A is a plan view illustrating the printed-circuit board, and FIG. 21B is a cross sectional view illustrating the same but viewed in the direction of arrows Exe2x80x94E.
Referring to FIGS. 21A and 21B, a ground pattern 101 and a power supply pattern 102 are formed, opposed to each other, in an insulating layer 103, and a signal wiring layer 104 is formed on the face and back of the insulating layer 103, and further a resistor 105 is provided at an end of the insulating layer 103 such that it is prevented from making any contact with the ground pattern 101 and the power supply pattern 102. The common mode current is suppressed owing to the resistor 105 to reduce the occurrence of EMI.
There are known, as the prior art printed-circuit board, ones where the common mode current is suppressed (a second prior art technique), ones where a high frequency loss material such as rubber ferrite is provided on the ground pattern and the power supply pattern such that it is in close contact with the latters. With the high frequency loss material the common mode current is suppressed to reduce the occurrence of EMI.
However the prior art printed-circuit board described above suffers from the following problems: In the first prior art technique the resistor 105 must be provided at the end of the insulating layer 103 with high accuracy such that it is prevented from making contact with the ground pattern 101 and the power supply pattern 102 thus causing a high manufacturing cost.
In the second prior art technique the material such as rubber ferrite that is the high frequency loss material is likely to be changed in its physical property (magnetic permeability) with the passage of time, so that the operation to suppress the common mode current becomes unstable.
In view of the above, it is an object of the present invention to provide a printed-circuit board, a coaxial cable, and an electronic device, which are capable of reducing the occurrence of EMI without a severe increase of the manufacturing cost by stably suppressing the common mode current.
According to a first aspect of the present invention, there is provided a printed-circuit board including:
a printed-circuit board including:
an insulating layer;
a wide electric conductor pattern formed into a plane configuration having a recessed section in part so as to make up a ground pattern or a power supply pattern on the insulating layer; and
an an additional electric conductor electrically connected with the wide electric conductor pattern so as to close the recessed section.
In the foregoing first aspect, a preferable mode is one wherein the wide electric conductor pattern comprises a T-shaped pattern, an L-shaped pattern, or an H-shaped pattern.
Another preferable mode is one wherein the wide electric conductor pattern and the additional electric conductor are formed on different surfaces of the insulating layer respectively.
Still another preferable mode is one wherein the wide electric conductor pattern and the additional electric conductor are electrically connected with each other through a via plug formed on the insulating layer.
Additional preferable mode is one wherein the additional electric conductor is electrically connected with a side surface of the electronic components of the wide electric conductor pattern at a position of packaging of the electronic components.
Further preferable mode is one wherein the additional electric conductor is electrically connected with a side surface of the wide electric conductor pattern on at least one side of the wide electric conductor pattern in a longitudinal direction of the wide electric conductor pattern.
Still further preferable mode is one wherein, the additional electric conductor is formed on the insulating layer simultaneously with the wide electric conductor pattern.
According to a second aspect of the present invention, there is provided a printed-circuit board including:
an insulating layer;
a wide electric conductor pattern making up a ground pattern or a power supply pattern;
a micro-strip line formed through the insulating layer on the wide conductor pattern; and
an additional electric conductor electrically connected with the wide electric conductor pattern on a side surface of at least one side of the micro-strip line.
According to a third aspect of the present invention, there is provided a coaxial cable including:
an insulating layer;
a core line;
a shield line formed around the core line through the insulating layer; and
an additional electric conductor electrically connected to at least one side in a length direction of the shield line.
In the foregoing second aspect, a preferable mode is one wherein a longitudinal size D of an outer peripheral edge of the additional electric conductor and a diameter d of the coaxial cable are set to satisfy a relationship: D=6d.
According to a fourth aspect of the present invention, there is provided an electronic device including:
a printed-circuit board including:
an insulating layer;
a wide electric conductor pattern formed into a plane configuration having a recessed section in part so as to make up a ground pattern or a power supply pattern on the insulating layer; and
an additional electric conductor electrically connected with the wide electric conductor pattern so as to close the recessed section; and
a coaxial cable including:
an insulating layer;
a core line;
a shield line formed around the core line through the insulating layer; and
an additional electric conductor electrically connected to at least one side in the length direction of the shield line.
According to a fifth aspect of the present invention, there is provided an electronic device including:
a printed-circuit board including:
an insulating layer;
a wide electric conductor pattern making up a ground pattern or a power supply pattern;
a micro-strip line formed through the insulating layer on the wide conductor pattern; and
an additional electric conductor electrically connected with the wide electric conductor pattern on a side surface of at least one side of the micro-strip line.
a coaxial cable including:
an insulating layer;
a core line;
a shield line formed around the core line through the insulating layer; and
an additional electric conductor electrically connected to at least one side in the length direction of the shield line.
According to a sixth aspect of the present invention, there is provided an electronic device in which at least one electronic component is mounted on a printed-circuit board wherein a planar wide electric conductor pattern making up a ground pattern or a power supply pattern is formed, the electronic device including:
an additional electric conductor electrically connected with an outer peripheral edge of the wide electric conductor pattern of a side surface of the electronic components so as to surround a mounted position of the electronic component.
With the above configurations, the additional electric conductor is electronically connected with the wide electric conductor pattern having a recessed section in part thereof so as to close the recessed section for increasing the width of the outer edge section of the wide electric conductor pattern so as to surround the recessed section with the additional electric conductor. Hereby, when the electronic components are packaged on the printed-circuit board, the radiated emission upon the common mode resonance is successfully suppressed.
With configurations of the above coaxial cable, a shield pattern is formed through the insulating layer around the core line, and the width of an outer edge section of the shield pattern is widened so as to surround the shield pattern with the additional electric conductor by electrically connecting the additional electric conductor with at least one side of the shield pattern. Therefore, when the electronic components are packaged on the coaxial cable, the radiated emission in the common mode resonance is successfully suppressed.
With configurations of the above electronic device, it is successfully operated without being influenced by the radiated emission in the common mode resonance because it is assembled with the printed-circuit board of the coaxial cable constructed reduce the radiated emission in the common mode resonance.
Thus, the common mode current is stably suppressed to reduce the occurrence of the EMI without severely increasing the manufacturing cost.
In the following, a principle of the present invention will be described, which is an opportunity of the achievement of the present invention.
The inventors associated with the present application performed an experiment and have found the following result. A printed-circuit board is provided on which there is formed a ground pattern or a power supply pattern including respectively a wide electric conductor pattern and a T-shaped pattern. In the printed-circuit board the inventors have found that unnecessary electromagnetic waves radiated from the wide electric conductor pattern are weakened upon common mode resonance by electrically connecting a frame-shaped additional electric conductor to the T-shaped pattern so as to close a recessed section and increasing a width of an external edge section. Accordingly, by electrically connecting the frame-shaped additional electric conductor to the wide electric conductor pattern having the recessed section in part of the T-shaped pattern, or a like, so as to close the recessed section to form the ground pattern or the power supply pattern. The principle of the present invention will be described below based upon an experimental result.
Referring now to FIG. 1A, which is a plan view illustrating a printed-circuit board 1 that includes a T-shaped pattern formed thereon, the printed-circuit board 1 is prepared, in which there are integrated a first electric conductor section 2 and a second electric conductor section 3 to form the T-shaped pattern, the first electric conductor section 2 being of a wide electric conductor pattern which is a rectangle of a size of 80 mm in a lateral direction X and a size of 100 mm in a longitudinal direction Y and the second electric conductor section 3 being of a wide electric conductor pattern which is a rectangle of a size of 60 mm in the lateral direction X and a size of 180 mm in the longitudinal direction Y, and in which a ground pattern 4 including the T-shaped pattern is formed on the surface of an insulating layer 5.
Referring further to FIG. 11, which is a plan view illustrating a printed-circuit board 10 in which a frame-shaped additional electric conductor is electrically connected to the T-shaped pattern so as to close a recessed section 6, the printed-circuit board 10 is prepared, in which the ground pattern 4 including the T-shaped pattern having the same size as that in FIG. 1A is formed on the surface of the insulating layer 5, and a frame-shaped additional electric conductor 7 is electrically connected to the T-shaped pattern of the ground pattern 4 so as to close the recessed section 6. The width size W of the frame-shaped additional electric conductor 7 is set to {fraction (1/10)} to {fraction (1/200)} (in the present example 140 mm) of the size of the ground pattern 4 in the lateral direction X, the ground pattern 4 including the T-shaped pattern.
Referring furthermore to FIG. 1C, which is a cross sectional view taken along arrows Axe2x80x94A, and in which a power supply pattern 8 is formed facing the ground pattern 4 in the insulating layer 5, and a wiring pattern (signal line) 9 is formed on a face and a back of the insulating layer 5.
As materials for the ground pattern 4, power supply pattern 8, wiring pattern, or a like, use is made of metals such as copper(Cu), aluminum (Al), and iron (Fe). As the insulating layer 5 use is made of an organic insulating board including epoxy resin and an inorganic insulating board including ceramics, or a like
Following is the T-shaped pattern (hereinafter, referred to as a wide electric conductor pattern.) that constitutes the ground pattern 4 described above with reference to FIGS. 1A, 1B and 1C. First, reviewing a common mode resonance where the size L in a lateral direction X is taken as a half wavelength, it is found from Maxwell equations that although a common mode current I flowing in the lateral direction flows, substantially half a common mode current I is concentrated in a region of substantially 15% of a distance extending from a electric conductor end up to a position of a center of the electric conductor in the longitudinal direction Y. The substantially half common mode current I flows in a vicinity of a contour line of the wide electric conductor pattern in such a fashion, so that the length of the contour line of the wide electric conductor pattern presents sharp influence on the common mode resonance.
Mounting of electronic components packaged on the wide electric conductor pattern causes an electric potential difference of high frequency to happen between the power supply terminal (not shown) and a ground terminal (not shown) to conduct a high frequency current, when electronic components generate a high speed pulse signal. Waves of current pattern reach a whole of the wide electric conductor pattern around the position of the electronic components. Current waves transmitted as such are reflected on a peripheral edge of the wide electric conductor pattern to cause a resonance current in the wide electric conductor pattern and hence cause the common mode resonance.
Provided there is formed a first electric conductor section 2 having narrow width as in the T-shaped pattern that constitutes the ground pattern 4, the common mode resonance is increased to radiate more radiation noise, that is radiated emission. The electronic components are packaged substantially at a center of the ground pattern 4 of the printed-circuit board 1, and the power supply terminal thereof and the ground terminal thereof are arranged in left and right directions.
Radiation electric power P1 obtained in this situation is more increased than in radiation electric power P2 where electronic components are packaged on the wide electric conductor pattern that forms an infinite plane. The radiation electric power P1 is computed with an electromagnetic simulation, and a radiation ratio P1/P2 is calculated by dividing the radiation electric power P1 by the radiation electric power P2 to demonstrate a characteristic curve B in FIG. 2, which illustrates a relationship between the radiation ratio (longitudinal axis) and frequencies (lateral axis), that is to say, frequency dependency of the radiation ratio.
As shown in FIG. 2, the radiation ratio is maximum at the frequency of 800 MHz, and the electronic components packaged on the printed-circuit board 1 generate radiated emission of about four times that of the electronic components packaged on the infinite plane wide electric conductor pattern.
In contrast, there are compared the radiation electric power P1 upon the electronic components being packaged on the printed-circuit board 10 illustrated in FIG. 1B and the radiation electric power P2 upon the electronic components being packaged on the wide electric conductor pattern that forms an infinite plane to obtain characteristics of a radiation ratio A as shown in FIG. 2.
As clarified in FIG. 2, characteristics of the radiation ratio A are substantially the same with the radiation ratio at the frequency of about 800 MHz being maximum. However, the radiation ratio is reduced to halt the situation with the characteristic of a radiation ratio B or lower.
More specifically, as illustrated in FIG. 1B, the radiated emission caused upon the common mode resonance can be suppressed to half or lower by packaging the electronic components by the use of the printed-circuit board 10 in which the frame-shaped additional electric conductor 7 is electrically connected with the T-shaped pattern of the ground pattern 4 to close the recessed section 6 compared with the case where the electronic components are packaged on the printed-circuit board 1 that includes the ground pattern 4 composed of the simple T-shaped pattern as illustrated in FIG. 1A. The width size W of the frame-shaped additional electric conductor 7 electrically connected to the wide electric conductor pattern composed of the T-shaped pattern is set to {fraction (1/10)} to {fraction (1/200)} (in the present example 140 mm) of the size of the ground pattern 4 composed of the T-shaped pattern in the lateral direction Y, and is presented to an electromagnetic simulation. For a reduction effect of the radiated emission, the just-mentioned cases are substantially the same as a case where a rectangular electric conductor is added. A reason is that impedance in a resonance of an antenna is substantially not influenced by a thickness of an antenna wire.